1. Field of the Invention
The present invention relates to a control system for an automobile engine equipped with an automatic transmission and, more particularly, to an automobile engine control system for controlling the beginning and end points of a engine torque dropping control during a downshift of the automatic transmission to reduce shift shocks due to torque changes.
2. Description of Related Art
Typically, an automobile engine equipped with an automotive transmission is controlled so that its output torque drops at a predetermined time, particularly during a downshift of the automatic transmission, so as to avoid shift shocks due to engine output torque changes. In controlling the proper times at which dropping of the engine output torque begins or ends during a downshift of the automatic transmission, it is generally determined that the proper time at which the automatic transmission begins to shift itself down should be based on a change in rotational speed of a turbine of the automatic transmission (which is referred to as turbine speed). The turbine speed at which engine torque dropping control is commenced or finished is obtained from the change in turbine speed multiplied by coefficients which are predetermined according to a particular downshift pattern. Such an engine control system is not known from, for instance, Japanese Unexamined Patent Publication No. 55-69,738.
In a conventional timing control for dropping engine output torque, however, since changes in engine output torque are caused by environmental conditions, such as atmospheric pressure and the temperature of intake air, the time necessary to change the turbine speed and shift the automatic transmission changes. As a result, a calculated turbine speed has an error relative to an actual turbine speed, so that dropping of the engine output torque is executed at a proper time. This results in producing shift shocks in the automatic transmission.
In addition, in the conventional timing control mentioned above, since a shift point is set up according to one of several shift patterns, it is not possible to obtain the proper times at which the engine output torque should begin to drop and finish dropping during a downshift of the automatic transmission.